Enhanced catalytic performance of trimethylsilylated Ti-MWW zeolites for the liquid-phase epoxidation of propylene with H2O2

The titanosilicate zeolite catalyzed epoxidation of propylene with hydrogen peroxide (H2O2, HP) to propylene oxide (PO), the so-called HPPO, is more eco-efficient, compared to the chlorohydrin process and the epoxidation using organic hydroperoxides. However, the zeolite catalysts used in the HPPO process are easily deactivated, because the main byproduct propylene glycol (PG) and other heavy byproducts with high boiling points, derived from the solvolysis of PO, are deposited inside the zeolite micropores. In the present work, trimethylsilylated TiMWW zeolites, named Si-Ti-MWW, were developed for the HPPO process. In combination with the results from extensive characterizations for the prepared zeolites, it is found that the trimethylsilylation merely occurs on the external surface of Ti-MWW crystals and can significantly enhance the hydrophobicity, but not alter the coordination states of the Ti species and textural properties of the zeolites. The catalytic properties of Ti-MWW and Si-Ti-MWW were compared in propylene epoxidation. The results show that the solvolysis of PO to the byproducts can be effectively inhibited over the hydrophobic zeolite surface, making Si-Ti-MWW exhibit a much higher selectivity for PO and a much better stability and reusability than the parent Ti-MWW in the HPPO process. The current study, therefore, provides a new approach to develop efficient catalysts for the HPPO process.